This invention relates to materials used in the construction of buildings and structures, and particularly to composite material substitutes for wood studs and dimension lumber used in residential construction for walls, floor joist systems and rafters.
The framework for a conventional wall in residential construction ordinarily comprises two parallel, horizontal nominally 2 inch by 4 inch ("2.times.4") wood "plates" separated by a plurality of abutting vertical "studs", that is, boards which are nominally 2.times.4 by 9 feet long. The number of studs used in any particular application may vary depending on whether they are to be load bearing or non-load beating. Other dimension lumber, such as, 2 inch by 6 inch ("2.times.6") boards may be used instead of 2.times.4's to increase the wall thickness or provide greater strength.
Wood studs have been favored for their strength and ability to support load bearing surfaces as well as the ease with which they can be manufactured and the ease with which a wall can be framed using them. There is a standard and long-practiced method for framing a wall. The plates and studs are laid out on the floor and the studs are fastened to the plates by driving nails through the outwardly-facing surfaces of the plates into the top and bottom ends of each stud. The practice of this method in residential construction is widespread. Craftspersons have acquired specific tools, such as air-powered nailers, skills and experience necessary to practice this conventional framing method effectively, efficiently and quickly. However, disadvantages in wood studs are becoming more apparent, particularly in view of efficiency-driven, modem construction practices, unavailability of suitable wood materials and consumer preferences.
Wood studs are prone to warping and cracking, with time. They are also susceptible to rot, mildew and termite infestation. Fire safety mindfulness also fuels a continual search for cost effective, nonflammable stud materials.
Depletion of forest resources and ongoing efforts to conserve forest resources translate into diminished supply and increased costs for wood products. One result is there is less lumber available that meets industry standards. In particular, lumber derived from old growth timber, which until recent times was a major source of timber for studs, has become relatively scarce. Lumber from old growth timber readily met industry standards. The younger timber being used produces lumber that does not readily meet industry acceptance. Relative to old growth lumber, it has poor tensile strength and dimensional stability. As a consequence, studs derived from younger timber tend to warp and produce finished walls that are uneven and unsightly. More significantly the load bearing ability of such walls may be compromised.
The foregoing disadvantages and demands reflect an unfulfilled need for improved studs to replace the conventional wood stud used in residential construction. Sheet metal provide potential for improvement. C-shaped metal studs have been used in the construction of commercial buildings. In commercial construction they are assembled between elongate metal rails instead of the wood plates used in residential construction. Assembly of such commercial walls involves different materials, methods and tools than are used and accepted by craftspersons doing residential construction. While some attempts have been made to employ commercial-type metal framing in residential construction, the methods and materials used in commercial framing have not gained acceptance by residential craftspersons for several reasons. Commercial wall systems have proven to be cost prohibitive relative to residential wall systems. Residential craftspersons are also disinclined to retool. For example, in the "metal-stud to metal-rail" construction used in commercial wall framing, the stud is fastened by screws, as opposed to nails in the "wood-stud to wood-rail" system employed in residential construction. To remain competitive, craftspersons and contractors do not want to retool, expend more time or effort or otherwise raise costs.
While there have been some attempts to develop suitable sheet metal based studs for residential construction, generally these attempts have been unsuccessful in one or more respects.
For example, Daniels, U.S. Pat. No. 4,001,993, entitled "STEEL WALL STUD AND WALL FRAME EMPLOYING THE SAME," proposes a sheet metal stud having two parallel short sides, two concave, corrugated long sides thereby forming an enclosed channel having essentially standard stud outer dimensions. Wood blocks are located in the respective ends of the channels. This structure has a number of drawbacks. One drawback is that the enclosed structure is unduly difficult to insulate electrically, making compliance with building codes exceedingly difficult and costly. Another drawback is that the exposed edges at the ends of the stud can shear or sever the fibers in the abutting wood plates; therefore, protective strips of particle board must be attached along the abutting faces of the plates, adding labor and expense to the manufacture and use of the stud. Yet another drawback is that the sheet metal member does not attach to the plates in the much-preferred conventional fashion of driving two nails through the outward faces of the plates and into the abutting ends of the stud; rather, nails are driven into portions of sheet metal that extend beyond the end of the stud into face-to-face contact with the vertical faces of the plates. This structure requires extra flaming steps and doubles the nailing otherwise required to fasten the studs to the plates. Still another drawback of the Daniels' structure is that the enclosed corrugated channels of the metal stud complicate and increase the expense of manufacturing and using the stud.
Johnson, U.S. Pat. No. 4,742,645, entitled "POCKET-DOOR ASSEMBLY," proposes sheet metal studs that attach to elongate metal headers for non-load bearing pocket doors which are located within, but are not a component of, partition walls. Each stud has a roughly C-shaped cross section. A piece of standard dimension lumber can be inserted into the stud, which has an interior width that is significantly greater in dimension than the inserted lumber piece and a centrally located recess for receiving and centrally positioning the lumber piece. The studs connect to a metal header by extension brackets having elements that slip within spaces formed between the inserted lumber pieces and the metal walls of the stud. Consequently, the studs of Johnson require relatively elaborate manufacturing steps and are relatively inconvenient to use. Moreover, the metal studs proposed by Johnson appear neither suitable for use as wall flaming material nor load bearing applications.
Accordingly, it can be seen that there is a need for an improved metal-based substitute for construction lumber, particularly 2.times.4 and 2.times.6 wall flaming material, that can be manufactured easily and inexpensively, attached to upper and lower plates by conventional flaming techniques, and relied on to support load bearing surfaces, without modification or damage to those surfaces.